Mix butter, oil and sugar till fluffy (about 2 minutes).
Add the pumpkin puree, mix gently.
Add the eggs one at a time until smooth.
Add flour 1/3 at a time till incorporated. The batter will be very thick. Spread in pan but don't worry if its lumpy, it will smooth out.
Bake for 1 hour to 1 hour 15 minutes. When knife comes out clean cool on a wire rake.